The present invention relates to an apparatus for granulating lumps of material, especially lumps of molded sand.
Reconditioning of used sand from a shake-out operation involves reducing used core elements and molded sand lumps to individual sand grains and removing the metallic particles, sintered clusters of sand grains, excess fines and other tramp and objectionable material. The quality of reclaimed sand must be comparable to that of new sand so that it may be satisfactorily substituted for new sand in sand mixtures without appreciable change in sand practice.
Foundries are adopting a practice utilizing quality sand, a chemical binder, and a catalyst which are mixed together and hardened into a solid cake at ambient temperatures to form a chemically bonded mold. Since baking is not required, this process is known in the art as "no-bake" molding. The no-bake molding process has distinct advantages such as ease of making a mold, cleaner environment, ease of handling a completed mold, and improved casting finishes and casting tolerances.
Despite the numerous advantages, there are a number of disadvantages, such as the increased cost for quality grade sand. Therefore, the effective and efficient reclamation of sand can play a significant part in making the no-bake molding process economically attractive. One of the steps in the reclamation of sand used in no-bake molding is the reduction of lumps of molded no-bake sand.
Prior art apparatus typically used for granulating lumpy material include hammermills, ring crushers, jaw or roll crushers which generally subject moving parts to excessive wear and stresses thereby decreasing machine life and increasing machine breakdowns. The large quantity of dust created by prior art apparatus is not only an undesirable pollutant but is evidence that the lumps are crushed to such an extent that a good yield of granulated material such as reclaimed sand is sacrificed.